Allow turning off linearity checks in bilinear and linear forms (#153)

Add the boolean flag `check_linearity` to the constructors of
`BilinearForm` and `LinearForm`. The default value is `True`. If set to
`False`, the linearity checks are turned off completely. This is
different than the existing flag `ignore_linearity_errors`, which
controls whether we get a warning or an error when the linearity check
fails.

The new flag might be useful when the expression in the bilinear or
linear form is complicated, because then the linearity check calls the
SymPy `Expr` method `.expand(deep=True)`, which is recursive and can
take a very long time.

---------

Co-authored-by: Yaman Güçlü <yaman.guclu@gmail.com>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name            = "sympde"
-version         = "0.18.2"
+version         = "0.18.3"
 description     = "Symbolic calculus for partial differential equations (and variational forms)"
 readme          = "README.rst"
 requires-python = ">= 3.8, < 3.12"

sympde/expr/expr.py

@@ -334,7 +334,7 @@ def space(self):
 class LinearForm(BasicForm):
     is_linear = True
 
-    def __new__(cls, arguments, expr, ignore_linearity_errors=False, **options):
+    def __new__(cls, arguments, expr, check_linearity=True, ignore_linearity_errors=False, **options):
 
         # Trivial case: null expression
         if expr == 0:
@@ -348,7 +348,7 @@ def __new__(cls, arguments, expr, ignore_linearity_errors=False, **options):
         args = _sanitize_arguments(arguments, is_linear=True)
 
         # Check linearity with respect to the given arguments
-        if not is_linear_expression(expr, args):
+        if check_linearity and not is_linear_expression(expr, args):
             print(expr)
             print(args)
             msg = f'Expression is not linear w.r.t. [{args}]'
@@ -419,7 +419,7 @@ class BilinearForm(BasicForm):
     is_bilinear = True
     _is_symmetric = None
 
-    def __new__(cls, arguments, expr, ignore_linearity_errors=False, **options):
+    def __new__(cls, arguments, expr, check_linearity=True, ignore_linearity_errors=False, **options):
 
         # Trivial case: null expression
         if expr == 0:
@@ -437,7 +437,7 @@ def __new__(cls, arguments, expr, ignore_linearity_errors=False, **options):
         trial_functions, test_functions = args
 
         # Check linearity with respect to trial functions
-        if not is_linear_expression(expr, trial_functions):
+        if check_linearity and not is_linear_expression(expr, trial_functions):
             msg = f'Expression is not linear w.r.t. trial functions [{trial_functions}]'
             if ignore_linearity_errors:
                 print(msg)
@@ -446,7 +446,7 @@ def __new__(cls, arguments, expr, ignore_linearity_errors=False, **options):
 
 
         # Check linearity with respect to test functions
-        if not is_linear_expression(expr, test_functions):
+        if check_linearity and not is_linear_expression(expr, test_functions):
             msg = f'Expression is not linear w.r.t. test functions [{test_functions}]'
             if ignore_linearity_errors:
                 print(msg)